The present invention relates to a sheet for preventing a leakage electric field of low frequency which is produced from a fluorescent tube cable of a liquid crystal display device, and also relates to a liquid crystal display unit and a liquid crystal display device, including the sheet.
In a liquid crystal display device which displays an image by controlling the driving of liquid crystal and the emission of light from a fluorescent tube, based on image data, in order to apply a high voltage to the fluorescent tube, an inputted low voltage is converted into a high voltage by an inverter and the resulting high voltage is supplied to the fluorescent tube through a fluorescent tube cable. In such a liquid crystal display device, a leakage electric field of low frequency is produced from the fluorescent tube cable which serves as a path of the high voltage. This leakage electric field is a noise component, and may disturb the realization of a stable display condition. It is therefore necessary to take some measures to prevent such a leakage electric field.
FIG. 1 and FIG. 2 are the exploded perspective view and side view of a conventional liquid crystal display unit adopting measures to prevent a leakage electric field. This liquid crystal display unit is configured by superimposing a liquid crystal display panel 21, a sheet metal shield member 22, an inverter printed board 23, and a covering shield member 24 in this order.
The liquid crystal display panel 21 has a flat body including a glass plate on its display surface side (front-face side) and a plastic plate on both of the non-display surface side (rear-face side) and the side-face side. Fluorescent tubes are attached to the upper and lower edges inside the liquid crystal display panel 21, respectively. Two bundles of fluorescent tube cables 25 composed of a plurality of thin wires for supplying a high voltage to the respective fluorescent tubes are connected to the fluorescent tubes, and each fluorescent tube cable 25 is extended to the non-display surface side (rear-face side) of the liquid crystal display panel 21. Moreover, screw holes 21a for attachment are formed in the four corners of the liquid crystal display panel 21.
The sheet metal shield member 22 has a flat body made of metal without a lid, and is placed to cover the non-display surface (rear face) of the liquid crystal display panel 21. The sheet metal shield member 22 has two cut holes 22a for pulling out the respective fluorescent tube cables 25 to the inverter printed board 23 side, and screw holes 22b in two positions. On the inverter printed board 23, an inverter circuit for converting an inputted DC voltage into an AC voltage is printed. The inverter printed board 23 has two connecting parts 23a serving as high voltage outputting parts to which the fluorescent tube cables 25 are connected respectively. Furthermore, the inverter printed board 23 has screw holes 23b which are formed in two positions corresponding to the screw holes 22b. The covering shield member 24 has a flat body made of metal without a lid, and is placed to cover the rear face of the sheet metal shield member 22. The covering shield member 24 has screw holes 24a in two positions corresponding to the screw holes 22b and the screw holes 23b. 
A conventional liquid crystal display unit is assembled as follows. In a state where the fluorescent tube cables 25 are pulled out from the cut holes 22a of the sheet metal shield member 22 to the inverter printed board 23 side, the non-display surface (rear face) of the liquid crystal display panel 21 is covered with the sheet metal shield member 22, and screws 26 are inserted into the screw holes 21a and screwed into the sheet metal shield member 22 so as to attach and secure the sheet metal shield member 22 to the liquid crystal display panel 21. The tips (connectors) of the fluorescent tube cables 25 pulled out from the cut holes 22a are connected to the connecting parts 23a of the inverter printed board 23. Then, the sheet metal shield member 22 is covered with the covering shield member 24 with the inverter printed board 23 between them, and screws 27 are inserted into the screw holes 24a, the screw holes 23b and the screw holes 22b so as to attach and secure the inverter printed board 23 and the covering shield member 24 to the sheet metal shield member 22 with the screws 27. Note that a protective insulating sheet may also be placed between the sheet metal shield member 22 and the inverter printed board 23.
In such a conventional liquid crystal display unit, the fluorescent tube cables 25 extended to the non-display surface side (rear-face side) of the liquid crystal display panel 21 are covered with the sheet metal shield member 22, and the fluorescent tube cables 25 pulled out from the cut holes 22a are covered with the covering shield member 24, so that leakage electric fields of low frequency which are produced from the fluorescent tube cables 25 are prevented by the presence of the sheet metal shield member 22 and covering shield member 24.
In the conventional liquid crystal display unit, since a sheet metal shield member, a covering shield member etc. are included so as to prevent a leakage electric field from a fluorescent tube cable, there is a problem that the overall thickness of the liquid crystal display unit becomes thicker. Moreover, since such shield members are essential, there is also a problem of high cost.
The present invention has been made with the aim of solving the above problems, and it is an object thereof to provide a leakage electric field preventing sheet capable of preventing a leakage electric field from a fluorescent tube cable without including a shield member like those used conventionally and of significantly reducing the thickness of a liquid crystal display unit and a liquid crystal display device, and to provide a liquid crystal display unit and a liquid crystal display device, including the sheet.
Another object of the present invention is to provide a leakage electric field preventing sheet capable of reducing the costs of a liquid crystal display unit and a liquid crystal display device because it does not require a shield member like those used conventionally, and to provide a liquid crystal display unit and a liquid crystal display device, including the sheet.
A leakage electric field preventing sheet according to the first aspect of the present invention is a non-conductive sheet for preventing a leakage electric field which is produced from a fluorescent tube cable for supplying electric power to one or a plurality of fluorescent tubes attached to a liquid crystal display panel having a conductive non-display surface at the opposite side of a display surface, and is configured so as to bring the fluorescent tube cable into contact with the non-display surface of the liquid crystal display panel. The leakage electric field preventing sheet of the first aspect is a non-conductive sheet, and brings the fluorescent tube cable extended from the conductive non-display surface side (rear-face side) of the liquid crystal display panel into contact with the conductive non-display surface of the liquid crystal display panel. Accordingly, the fluorescent tube cable can be grounded on the conductive non-display surface of the liquid crystal display panel. It is therefore possible to efficiently prevent a leakage electric field from the fluorescent tube cable in a simple manner without using shield members as in the conventional example.
A leakage electric field preventing sheet according to the second aspect of the present invention is based on the first aspect, and comprises a notch portion for holding the fluorescent tube cable. The leakage electric field preventing sheet of the second aspect holds the fluorescent tube cable extended from the conductive non-display surface side (rear-face side) of the liquid crystal display panel with the notch portion. Thus, the leakage electric field preventing sheet certainly brings the fluorescent tube cable into contact with the conductive non-display surface of the liquid crystal display panel.
A liquid crystal display unit according to the third aspect of the present invention comprises: a liquid crystal display panel including one or a plurality of fluorescent tubes; a fluorescent tube cable for supplying electric power to the fluorescent tube; a leakage electric field preventing sheet of the first or second aspect; and an inverter printed board connected to the fluorescent tube cable. The liquid crystal display unit of the third aspect prevents a leakage electric field from the fluorescent tube cable by using the above-mentioned leakage electric field preventing sheet of the first or second aspect, and therefore shield members which are used in the conventional example are unnecessary, and both the thickness and the cost of the liquid crystal display unit are reduced.
A liquid crystal display device according to the fourth aspect of the present invention is a liquid crystal display device for displaying an image by driving a liquid crystal, and comprises a liquid crystal display unit of the third aspect. The liquid crystal display device of the fourth aspect comprises the above-mentioned liquid crystal display unit of the third aspect which prevents a leakage electric field from the fluorescent tube cable in a simple manner, and therefore shield members which are used in the conventional example are unnecessary, and both the thickness and the cost of the liquid crystal display device are reduced.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.